High power r.-f. switch tube



1957 0. F. FOlN, JR

HIGH POWER R.F. SWITCH TUBE Filed 001;. 26, 1948 TO UTILIZATION CIRCUIT FROM HIGH POWER SOURCE INVENTOIL OWEN F. FOIN JR.

United States Patent iOfiice 2,813,999 Patented Nov. 19, 1957 HIGH POWER R.-F. SWITCH TUBE Owen F. Foin, Jr., Fresno, Calif.

Application October 26, 1948, Serial No. 56,602

1 Claim. (Cl. 315-39) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates to switching devices and more particularly to devices for switching high power electromagnetic energy.

Devices provided heretofore for controlling the transmission of electromagnetic energy through mechanical transmission mediums are incapable of switching high power electromagnetic energy due to inherent characteristics which render the devices responsive to the energy to be switched. For example, prior devices employ a tuned cavity including discharge means therein responsive to an external control source for destroying the resonant condition of the cavity and producing an effective switching impedance across the transmission medium. In such devices, the discharge means is inherently responsive to the electromagnetic energy field within the cavity so that a discharge occurs, independently of the external control source, when the power of the transmitted energy exceeds a permissible level. Consequently, such prior devices are incapable of switching high power electromagnetic energy solely in accordance with an external controlling influence.

It is therefore an object of the present invention to provide novel means for switching high power electromagnetic energy.

Another object is to provide a device for switching high power electromagnetic energy in accordance with a predetermined controlling influence independently of the power of the energy to be switched.

Another object is to provide a novel arrangement for selectively controlling the transmission of high power electromagnetic energy through operation of an electronic device inherently non-responsive to the power of the transmitted energy.

Still another object of the present invention is to provide a novel device for switching a mechanical transmission medium to control transmission of high power electromagnetic energy therethrough, which incorporates impedance transforming means in the form of a tuned cavity structure connected to the medium to normally reflect a certain impedance condition thereto, with electron discharge means associated with the cavity structure inherently non-responsive to the power of the energy and operable in accordance with a predetermined controlling influence so that an impedance is established in said medium of a value equal to the inverse of said normally reflected impedance.

Still another object is to provide a switching device having the foregoing characteristics wherein the electron discharge means includes a device for producing an electron discharge in response to ionization of gas included within the cavity structure and means for preventing ionization of the gas in response to the high power ener gy to be switched.

A still further object of the present invention is to provide a device for switching electromagnetic energy independently of the power thereof comprising ion discharge means for eifecting the switching function which includes a source of electrons without the cavity and normally isolated therefrom.

Other objects and features of the present invention will become apparent upon consideration of the follow ing detailed description in connection with the accompanying drawing which discloses one embodiment of the invention. It is to be expressly understood however that the drawing is designed for purposes of illustration only and not as a definition of the limits of the invention, reference for the latter purpose being had to the appended claim.

In the drawing, wherein similar reference characters denote similar elements through the several views:

Fig. 1 is a diagrammatic sectional illustration of a switching device embodying the principles of the present invention, and

Fig. 2 is a sectional illustration through line 22 of Fig. 1.

With reference more particularly to Fig. 1 of the drawing a switching device constructed in accordance with the principles of the present invention is disclosed therein in connection with a mechanical transmission medium It} for controlling the transfer of high power electromagnetic energy therethrough. The mechanical transmission medium 10 is disclosed in the form of a metallic hollow wave guide having rectangular cross section, however, it is to be expressly understood that the present invention may be employed in connection with other forms of mechanical transmission mediums well known to those skilled in the art. The mechanical transmission medium 10 is energized from a source of high power energy, not shown, such as an ultra-high radio frequency generator, and functions to transmit such energy to a utilization circuit, which may take the form of a radiating element, not shown in a conventional manner.

The novel switching device includes a tuned cavity 11 coupled to the mechanical transmission medium 10. The cavity 11 is disclosed in the form of a predetermined length of hollow metallic wave guide having rectangular cross section, with one end thereof coupled to the mechanical transmission. medium 10 through a coupling iris 12 and with the end thereof remote from the medium 10 short-circuited by a transverse metallic wall 13. The coupling iris 12 is provided with a dielectric window 14 for allowing the cavity to be evacuated through a tubulation 15 and subsequently filled with an ionizable gas under suitable pressure.

The physical dimensions of the cavity 11 are determined in accordance with the mean frequency of the energizing high power energy. In particular, the physical length of the cavity 11 between the iris 12 and the metallic wall 13 corresponds to a predetermined wave length of the high power energy so that a certain effective impedance condition is normally established in the mechanical transmission medium 10. It is to be understood that conventional tuning means may be associated with the cavity 11 to accurately establish the dimensions thereof. If the mechanical transmission medium 10 comprises a hollow rectangular wave guide operating on the TE01 mode, and an H type or parallel connection exists between the cavity 11 and the. wave guide, an open circuit will be maintained across the wave guide when the metallic wall 13 is spaced from the iris 12 by a distance equal to an odd multiple of quarter wave lengths of the mean operating frequency, as disclosed. Under such conditions, maximum transmission of energy occurs through the medium 10.

As mentioned heretofore, it is an object of th present invention to provide a switching device for controlling the transmission of high power energy through the medium 10 in accordance with a predetermined controlling influence and independently of the transmitted energy. The foregoing is accomplished by providing electron discharge means, non-responsive to and operable independently of transmitted energy, for establishing a shortcircuit across the cavity 11 a proper electrical distance from the coupling iris 12 to effect an impedance condition in the mediumwhich is an inverse of the impedance condition normally established therein. With an arrangement as disclosed in the drawing the shortcircuit produced across the cavity 11 is spaced an even multiple of electrical quarter wave lengths of the mean operating frequency so that the normally open circuit in the medium 10 is inverted to a short-circuit blocking energy transmission through the medium.

The electron discharge means includes a cathode 16 positioned outside the cavity 11 in a cathode chamber 17 formed by closed rectangular metallic extension 18 secured to wall 19 of the cavity 11. The cathode 16 is mounted in insulating material20 and is provided with a conventional heating element 21. An anode 22 is provided for collecting electrons emitted by the cathode 16. The anode 22 is mounted within the cavity 11 adjacent wall 23 thereofby means of insulating material 24. The electron discharge means further includes an electron control means positioned intermediate the cathode 16 and the anode 22. The control means includes a portion of the wall 19 having an aperture 25 therein lying in the normal electron path from the cathode 16 to the anode 22. A grid structure 26 is provided in the aperture 25 to effectuate electron control. The control means is maintained at ground potential, and electron fiow is determined by the potential of the cathode 16. The anode 22, the cathode 16 and the aperture 25 are positioned in a common plane parallel to the plane of the metallic wall 13 and spaced therefrom by a predetermined distance so that the electron discharge produced effectively reduces the electrical length of the cavity 11 by an odd multiple of quarter wave lengths of the mean operating frequency, as disclosed. With this arrangement, when electron discharge occurs, in a manner that will be described more fully hereinafter, the short-circuit produced thereby inverts the impedance condition normally existingin the medium 10.

The electron discharge means functions by controlling the potential of the cathode 16 in accordance with a predetermined controlling influence through operation of a control tube27. The anode of the tube 27 is directly connected to the cathode 16 and to a source of positive potential 28througlr a high value resistor 29. Thetube 27 is biased beyond cut-off by'means of grid resistor so that the cathode 16 is normally maintained at a potential determined by the source 28. When the tube 27 is rendered conducting, upon application of a positive impulse A to the grid thereof, the cathode 16 is effectively connected to ground potential. The potential source 28 is also connected to the anode 22 and is maintained at a value at least equal to the ionization potential of the gas included within the cavity 11.

Under normal conditions, that is, when the tube 27 is non-conducting, the cathode 16 is maintained at a potential substantially equal to the potential of the anode 22, and the control elements 19, 25 and 26, maintained at ground potential, function to completely isolate the electrons in the chamber 17 from the resonant cavity 11 and prevent ionization of the gas therein. Consequently, for reasons mentioned heretofore, high power energy is transmitted through the mechanical transmission medium 10 unimpeded by the switching device. In view of the factthat thesource of electronsinthe chamber 17 are isolated from the cavity, 11, that no means areprovided within the cavity 11'to produce a high voltage diiferential incident to the electromagnetic field within the cavity, and since the high voltage maintained on the anode 22 increases the impedance of an ion discharge that may tend to occur within the cavity 11, it is to be expressly understood that the switching device is wholly unresponsive to the transmitted energy irrespective of the power thereof.

When it is desired to prevent transmission of energy through the mechanical transmission medium 10 the tube 27 is rendered conducting, upon application of positive impulse A to the grid thereof, to connect the cathode 16 to ground potential. When. the potential of the cathode 16 drops to the potential of the electron control means 19, 25 and 26, electrons in the chamber 17 flow toward the high potential anode 22 at sufiicient velocity to produce ionization of the gas within the cavity 11 and effect a gas discharge between the cathode 16 and the anode 22. Such gas discharge eifectively short-circuits the cavity 11 in a plane parallel to the metallic wall 13 and spaced therefrom by an electrical distance equal to an odd multiple of quarter wave lengths of the main operating frequency. The electron discharge device is thus operable to produce a cavity which reflects a short-circuit across the medium 10 to prevent transmission of energy therethrough.

It is to be expressly understood that the switching function is solely dependent upon the control signals, such as the pulse A, applied to the grid of the control tube 27, since, as mentioned heretofore, the electron discharge means is non-responsive to power of transmitted energy and operates solely in response to potential variations of the cathode 16. Consequently, the duration of the switch on and switch off periods and the time interval required for the switching function is solely deter mined by the characteristics of the tube 27 and of the control signal input to the control grid thereof. The duration of the switch off period is dependent upon the length of applied pulses while the rapidity of the switching function is directly proportional to the tri ing time of the tube 27 and the slope of the control pulses. The control signals may be provided through the use of high speed keying equipment of conventional con struction when high speed switching is desired.

There is thus provided by the present invention a novel switching device for controlling transmission of hrgn power energy through a mechanical transmission medium, wherein the switching operation is solely responsive to a predetermined controlling influence and completely independent of the magnitude of the transmitted p The device is so characterized for operation in co. tion with high speed electronic keying equipment and possesses aninherently long life since high voltages are not necessarily required to effectuate the switching function.

Although only one embodiment of the present invention has been disclosed and described herein it is to be expressly understood that various changes and substitutions may be made therein without departing from the spirit of the invention as well understood by those skilled in the art. For example, as mentioned heretofore, various forms of mechanical transmission mediums may be controlled by employing a switching device embodying the principles of the present invention, while it is to be also understood that other conventional forms of im pedance transforming means may be utilized instead of the type disclosed. Moreover, it is to he expressiy understood that the. invention is not restricted to use in connection with wave guides operating on the TEQ], mode, or to arrangements wherein an H type or parallel connection exists between the impedance transformer and thewave guide, And'furthermore, it is to be und rstand that the arrangement may be such that transmission of energy is prevented when the switching device is in the normal or quiescent condition. Reference therefore will be had to the appended claim for a definition of the limits of the invention.

andused by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

In combination with a main waveguide and a gas filled switching stub section, means for electrically altering the effective length of said stub section to change the impedance reflected to said main waveguide comprising, an anode and a cathode located adjacent opposite walls of said stub section, a-blocking grid interposed between said anode and cathode and forming a part of one Wall of said stub section, impedance means for normally biasing said cathode positive with respect to said grid to prevent electron flow into said stub section, and electronically controlled means for varying said impedance means to cause electron flow and thereby produce ionization in said stub section.

References Cited in the file of this patent UNITED STATES PATENTS 2,403,302 Richmond July 2, 1946 2,403,303 Richmond July 2, 1946 2,412,892 Krasik Dec. 17, 1946 2,413,385 Schmidt Dec. 31, 1946 2,416,168 Fiske Feb. 18, 1947 2,423,998 Schantz July 15, 1947 2,491,971 Hall Dec. 20, 1949 2,501,545 Sproull Mar. 21, 1950 2,531,122 Fiske Nov. 21, 1950 OTHER REFERENCES Practical Analysis of Ultra High Frequency (RCA) by Meagher and Markley, published by R. C. A. Service Co. Inc., Camden, N. J., page 17. V 

